The present invention relates to the barrel-making or cooperage industry, and, in particular, to a machine which cuts staves for making barrels.
FIG. 1 shows a typical barrel 10 made up of staves 12 tied together with hoops 14. When producing a given type of barrel, all the barrels are made with the same number of staves. In order for the staves to fit together properly, the edges of the staves are cut with an angle alpha, shown in FIG. 3. This angle is called the flare angle. The angle alpha is 360.degree. divided by the number of staves in the barrel.
In order for the barrel 10 to have a barrel shape, with the center having a wider diameter than the ends, the staves 12 must be bowed, having a wider center than ends. FIG. 4 shows a stave 12, and the amount of bow, called the bilge, is shown at 16. The longitudinal axis 18 of the stave 12 is an imaginary line dividing the stave in half lengthwise. The grain of the wood in the stave runs lengthwise as well, parallel to the longitudinal axis 18. The midpoint 20 of the stave is halfway between the ends 22.
When the barrel is assembled, the flat staves are bowed and tied together with hoops 14. A cross-section of the assembled barrel is shown in FIG. 2.
The stave blanks which arrive at the barrel factory from the lumber mill have straight sides and ends as shown in dotted lines in FIGS. 3 and 4. At the barrel factory, the flare angle alpha and the bilge 16 must be cut into the stave blanks. In order for the barrels to be of high quality, the cuts must be very accurate on every stave. It is also important for the person operating the stave cutting machine to have good control of where the cut will be, to avoid wasting wood. It is also important for the cutting process to proceed quickly, in order to manufacture the staves efficiently.
The cooperage industry is a very old industry, and the prior art for stave-cutting machines goes back many years. Machines such as that shown in U.S. Pat. No. 942,799 "Taylor" (1909) have a saw on a horizontal carriage. In order to cut a stave lying horizontally, the saw blade rotates about an axis which is substantially horizontal but is tilted at the angle of the flare, and the carriage takes the saw along a track which follows the path of the bilge, so as to cut the properly-shaped edge on a stave. The saw cuts into the front face of the stave. Then the half-cut stave is removed from the machine, is turned around, and the saw makes another run along the track. In general, this type of machine is built to make only one size and shape of barrel. U.S. Pat. No. 186,704 "Arbey" (1877) also has a saw running horizontally, but it has the stave rocking back and forth to create the bilge.
It is also known to cut staves with a machine which has a large cutter wheel rotating about an almost horizontal axis (at a slight angle to provide the flare angle), with the wheel having angled knives projecting out of its front face. The horizontal stave is then pushed into the large cutter wheel, and, since the angled knives are farther away from the stave at the center than at the ends, the knives cut the bilge shape on the stave. Again, these machines are not adjustable. They are made to cut a single size and shape of stave. Also, they tend to waste wood, because it is very easy to push the stave into the cutter wheel too far, thereby cutting away more wood than necessary in making the stave. Because the cutter wheel in these machines is so large, it cannot rotate at very high speeds (rotates at about 800 rpm) and therefore tends to tear away chunks of wood, again wasting material. In this type of machine, as in other prior art machines, the cutter knives impact the stave's front face.